The invention relates generally to molecular sieves or filters. More particularly, the invention relates to carbon-containing molecular sieves and to a process of making the same.
It is known that coke having a certain volume of pores is suitable for adsorbing oxygen (O.sub.2) molecules preferentially to nitrogen (N.sub.2) molecules, that is, such coke is able to effect a certain separation of oxygen and nitrogen. The effective size or cross-section of the pores for effecting such a separation lies in the approximate range of 0.2 to 0.6 millimicrons. On the other hand, the pores in conventional coke have substantially larger cross-sections than this.
A manner of preparing molecular sieve coke which enables a gas mixture such as, for example, air, to be separated into a gas containing smaller gas molecules, for instance, oxygen, and a gas containing larger gas molecules, for instance, nitrogen, is also already known. Here, coke is heated to approximately 500 to 900.degree.C and a stream of carbonaceous gas is passed through the coke. Carbon splits off from the gas and is deposited in the effective pores of the coke thereby reducing the cross-sections of these pores to the order of 0.3 millimicrons.
While the process outlined above does cause a reduction in the size of the pores, there are certain problems associated therewith. Thus, this process requires painstaking temperature regulation. Moreover, the product resulting from the treatment with the carbonaceous gas must be cooled in an inert gas stream. Hence, the aforementioned process is not only troublesome but is also relatively expensive.